Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure
Reexamination Certificate
2001-08-09
2003-05-27
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
C257S010000, C257S011000, C257S013000, C257S014000, C257S019000, C257S021000, C257S022000, C257S080000, C257S081000, C257S082000, C257S083000, C257S184000, C257S185000, C257S186000
Reexamination Certificate
active
06570187
ABSTRACT:
TECHNICAL DOMAIN
The present invention concerns a light emitting and guiding device with an active region based on silicon, and processes for manufacturing such a device.
An active region is taken to mean a region of the device in which the light is generated and/or guided before leaving the device.
The invention finds applications in the manufacture of optical or optoelectronic components such as electroluminescent diodes, lasers, or possibly photodetectors.
A particularly advantageous application of the invention, linked to the use of silicon for the active region, is the manufacture of integrated circuits that combine both electronic components and optical components. Electronic components are in fact mainly manufactured from silicon, due to the intrinsic qualities of this semi-conductive material, and due to the widespread development of technologies relating to its applications.
PRIOR TECHNICAL SITUATION
As evoked above, silicon is very widely employed in the manufacture of electronic components or integrated circuits using semi-conductors.
However, in certain applications, in which components intended for light emission are used, silicon turns out to be unsuitable.
In fact, silicon is a semi-conductor with an indirect forbidden band and is not suitable for the rapid recombination of carriers, in other words, electron-hole pairs, with the production of light. When the elgctrons and the holes are brought together, for example when directly polarising a p-n junction formed in the silicon, their average recombination time can reach periods of several microseconds or even longer. In fact, the phenomenon of carrier recombination is dominated by other processes that are more rapid than the radiative recombination. These processes essentially correspond to the non-radiative recombination of the carriers on defects and impurities.
The defects and impurities play an important role, even if their concentration is low. The carriers move in the semi-conductor over a large distance and the probability of their encountering a defect or impurity is high.
Thus, in a certain number of applications, silicon must be replaced by another semi-conductive material with a direct forbidden band such as, for example, gallium arsenide (GaAs). As an indication, for this semi-conductor, the average recombination time of the electron-hole pairs is around one nanosecond.
Gallium arsenide is however an expensive material and more complex to implement.
In a certain number of specific cases, and in specific conditions of use, silicon has been proposed for making light emitting or conducting devices. Examples of such uses of silicon are proposed, in particular, in documents (1) to (7), whose references are detailed at the end of the present description.
The documents propose techniques that make it possible to increase the efficiency of light emission by silicon. Nevertheless, these techniques are not generally suited to the requirements of the integration of components.
In a more specific manner, documents (6) and (7) describe light emitting or conducting devices. Examples of such uses of silicon are proposed, in particular, in documents (1) to (9), whose references are detailed at the end of the present description.
The documents propose techniques that make it possible to increase the efficiency of light emission by silicon. Nevertheless, these techniques are not generally suited to the requirements of the integration of components.
In a more specific manner, documents (6) and (7) describe light emitting devices made on a silicon type substrate over an insulator (SOI—Silicon an Insulator), increasingly used in the micro-electronics field. However, the low temperature operating conditions and the isotropic character of the light emission of the devices also constitute obstacles to their use as components in circuits.
Documents (8) and (9) describe, respectively, a photon resonator and particular embodiments of silicon diodes doped with erbium.
DESCRIPTION OF THE INVENTION
The aim of the present invention is to propose a device capable of emitting but also guiding light, which is based on silicon and which can be manufactured according to common techniques specific to the micro-electronics field.
Another aim is to propose such a device that can be used as an individual component or as an integrated component in a circuit, in association with other optical or electronic components.
Another aim is to propose such a device with an improved light emission output and capable of operating at ambient temperature.
Another aim is to propose manufacturing processes for a device according to the invention.
In order to achieve these aims, the objective of the invention is more precisely an emitting and guiding device as defined in claim 1. Claims 2 to 16 indicate particular embodiments of the device.
The device described in the invention has the advantage of both confining the carriers within a restricted region, the active region, in such a way as to reduce the probability of the carriers encountering non-radiative centres, and the advantage of offering the carriers, in this region, radiative centres with a short life time.
A short life time is taken to mean a life time shorter than the life time linked to the probability of non-radiative recombination on defects or impurities in the active region.
The active region is, for example, a thin, continuous film of silicon stacked between the first and second insulator layers. This film is preferably mono-crystalline, which gives it better radiative qualities.
According to a particular embodiment of the device described in the invention, the means used to confine the carriers comprise the first and second insulator layers and the whole assembly, comprising the active region and the insulator layers, has an optical thickness e, whereby:
e
=
k
λ
2
and where k is a natural integer.
In this particular embodiment, adapted to a device operating at a given wavelength &lgr;, the light is confined in the active region. It propagates in the principal plane of this region, particularly in the case where the active region is a thin layer of silicon, by total reflection on the insulator layers. The principal plane is defined as a plane of the active region more or less parallel to that of the insulator layers.
The total reflection is obtained thanks to an appropriate step index between the material in the active region (Si) and the material used for the insulator layers (for example SiO
2
).
The optical thickness e of the layer or the active region in silicon is adapted to the working wavelength &lgr; in such a way that: e=k&lgr;/2, where k is an integral number.
According to a variant of the invention, the propagation can also be allowed to be perpendicular to the principal plane. In this case, the device can, moreover, comprise the means of reflecting the light comprising at least one mirror arranged on a free face of at least one of the first and second insulator layers.
More precisely, the means of reflecting the light can comprise a first mirror arranged on the free face of the first insulator layer and a second mirror arranged on the free face of the second insulator layer, with the first and second mirrors having different transmission coefficients.
The mirror with the highest transmission coefficient can then be used as a light exit mirror.
Moreover, the first and second mirrors can form a Fabry-pérot type cavity with the active region.
It should be pointed out that the means of reflection also have a function of guiding the light.
As indicated previously, the active region contains radiative centres, in other words, centres that allow the radiative recombination of the carriers.
Different types of radiative centres can be used and may possibly be combined in the active region.
A first type of radiative centre can be formed from the ions of rare earth elements, possibly accompanied by other impurities.
The rare earth elements, such as, for example, erbium, praseodymium or neodymium are efficient radiative recombination centres. The wavelength of the emitte
Hadji Emmanuel
Magnea Noël
Pautrat Jean-Louis
Ulmer Hélène
Commissariat a l′Energie Atomique
Flynn Nathan J.
Greene Pershelle
Pearne & Gordon LLP
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